Physics and Chemistry. 145 
The formula gives 
T = 20653°7, 
and consequently 
t = 20380°7. 
There are still two causes which can modify these results; but 
small, it is nevertheless certain that we receive the rays from sev- 
consider the absorption of the terrestrial nie oe nor much 
e into consider- 
. The Pseudophone.—For investigating the laws of Binaural 
Audition,* Professor 8. P. Tuomp U 
ment which he calls the psexdophone, and which, as he states, is 
acoustic perception of space. It consists of a Fg of ear-pieces 
furnis ed with adjustable metallic flaps or reflectors of sound, 
which can be fitted to the ears by straps and can be set at any 
desired angle with respect to the axis of the ears, and can also be 
turned upon a revolving collar about that axis so as to reflect 
Sounds into the ears from any desired direction. In regard to its 
use the author says: 
The estimate we are able to make of the position of a source of 
Sound, judging solely by the relative intensities of the sensation in 
the two ears, depends upon our previous perceptions and upon 
our possession of a constant amount of effective auditory surface, 
and a constant angle subtended between the ears and the line of 
Vision 
In the pseudophone these angles are variable, and the amount 
of effective sneak can also be varied, and this without any 
* See this Journal, vol. xvii, 64, 322. 
